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Peer-reviewedCC BY 4.0Molecules

UV-Induced Colour Changes in Bio-Based Coating Formulations Containing Turmeric and Madder Studied by EPR and FTIR

  • Wojciech Żyłka1
  • Barbara Pilch-Pitera2
  • Ireneusz Stefaniuk1
  1. 1Faculty of Exact and Technical Sciences, Institute of Materials Engineering, University of Rzeszow, Pigonia 1, 35-310 Rzeszow, Poland
  2. 2Department of Polymers and Biopolymers, Faculty of Chemistry, Rzeszów University of Technology, ul. Powstańców Warszawy 6, 35-959 Rzeszów, Poland
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Abstract

The study investigated the mechanism of colour change in coating formulations containing natural colorants—madder (Rubia tinctorum) and turmeric (Curcuma longa)—under UV irradiation using electron paramagnetic resonance (EPR) and Fourier-transform infrared spectroscopy (FTIR). Samples based on Epidian® 5 epoxy resin and Polimal® 109 unsaturated polyester resin containing radical and cationic photoinitiators were examined. EPR analysis revealed the involvement of transition metal ions (Fe3+, Cu2+) and organic radicals in the photo-oxidation processes. Characteristic signals at g ≈ 4.3, g = 2.2–2.3 and g = 2.001 were attributed to Fe3+, Cu2+ and aromatic radicals, respectively. UV irradiation caused the formation of oxygen- and phenoxyl-type radicals in turmeric-containing epoxy coatings and phenoxyl and semiquinone radicals in madder-containing coatings. The colour changes correlated with structural transformations identified by FTIR spectroscopy, while polyester coatings showed slower colour-change dynamics. The results confirm the usefulness of EPR and FTIR spectroscopy for analyzing UV-induced processes in polymer coating formulations containing plant-derived colorants and provide insight into the photochemical stability of bio-based components considered for more environmentally friendly coating materials.

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Cite

BibTeXRIS
BibTeX
@article{zylka2026uvinduced,
  title = {{UV-Induced Colour Changes in Bio-Based Coating Formulations Containing Turmeric and Madder Studied by EPR and FTIR}},
  author = {Wojciech Żyłka and Barbara Pilch-Pitera and Ireneusz Stefaniuk},
  journal = {Molecules},
  year = {2026},
  month = nov,
  doi = {10.3390/molecules31213930},
  url = {https://www.mdpi.com/1420-3049/31/21/3930},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - UV-Induced Colour Changes in Bio-Based Coating Formulations Containing Turmeric and Madder Studied by EPR and FTIR
AU  - Wojciech Żyłka
AU  - Barbara Pilch-Pitera
AU  - Ireneusz Stefaniuk
PY  - 2026
DA  - 2026/11/01
JO  - Molecules
DO  - 10.3390/molecules31213930
UR  - https://www.mdpi.com/1420-3049/31/21/3930
AB  - The study investigated the mechanism of colour change in coating formulations containing natural colorants—madder (Rubia tinctorum) and turmeric (Curcuma longa)—under UV irradiation using electron paramagnetic resonance (EPR) and Fourier-transform infrared spectroscopy (FTIR). Samples based on Epidian® 5 epoxy resin and Polimal® 109 unsaturated polyester resin containing radical and cationic photoinitiators were examined. EPR analysis revealed the involvement of transition metal ions (Fe3+, Cu2+) and organic radicals in the photo-oxidation processes. Characteristic signals at g ≈ 4.3, g = 2.2–2.3 and g = 2.001 were attributed to Fe3+, Cu2+ and aromatic radicals, respectively. UV irradiation caused the formation of oxygen- and phenoxyl-type radicals in turmeric-containing epoxy coatings and phenoxyl and semiquinone radicals in madder-containing coatings. The colour changes correlated with structural transformations identified by FTIR spectroscopy, while polyester coatings showed slower colour-change dynamics. The results confirm the usefulness of EPR and FTIR spectroscopy for analyzing UV-induced processes in polymer coating formulations containing plant-derived colorants and provide insight into the photochemical stability of bio-based components considered for more environmentally friendly coating materials.
SN  - 1420-3049
ER  -